Dealing with Potato Scab

Potato scab causes rough, corky patches on tuber skins—making potatoes unsightly, though usually still edible. Understanding what causes scab and how to prevent it will help you grow smoother, healthier spuds.

What is Potato Scab?

• Common scab (Streptomyces scabies):
  Bacterial infection that thrives in dry, alkaline soils and attacks developing tubers.
• Symptoms:
  Brown, raised, tough lesions or “scabs” on the skin. Sometimes deep pitting.

How to Prevent Potato Scab

• Soil pH:
  Scab loves alkaline soils. Test your soil—aim for pH 5.5–6.0.
  • Avoid liming your potato bed before planting.
• Organic Matter:
  Enrich soil with compost or well-rotted manure to hold moisture and encourage healthy soil bacteria.
• Irrigation:
  Water evenly and consistently during tuber formation. Dry soil at this stage drastically increases scab risk.
• Resistant Varieties:
  Grow scab-resistant potatoes like ‘Maris Piper’, ‘Estima’, ‘King Edward’, and ‘Cara’.
• Rotation:
  Rotate crops—a 3- to 4-year break from potatoes in the same spot helps prevent scab build-up.

Reducing Scab If It Strikes

• Avoid overhead irrigation (which can spread spores).
• Harvest potatoes when mature, not overly late.
• Wash and peel if lesions are only skin-deep. Deep-pitted potatoes are best used first.

Is Scab Harmful?

• Potato scab doesn’t affect flavor or edibility—simply peel the rough skin.
• Not dangerous to humans, just unsightly.

Bonus Tips

• Don’t plant potatoes after root crops (like carrots or beets)—these can increase scab risk.
• Add leaf mold or pine needles to make soil more acidic before planting (if needed).